The University of Toledo The University of Toledo Digital Repository Theses and Dissertations 2013 The roles of individual differences and working memory in episodic memory Aparna A. Sahu The University of Toledo Follow this and additional works at: http://utdr.edu/theses-dissertations Recommended Citation Sahu, Aparna A., "The roles of individual differences and working memory in episodic memory" (2013). Theses and Dissertations. This Dissertation is brought to you for free and open access by The University of Toledo Digital Repository.
It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of The University of Toledo Digital Repository. For more information, please see the repository's About page. A Dissertation entitled The Roles of Individual Differences and Working Memory in Episodic Memory by Aparna A Sahu Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Experimental Psychology _________________________________________ Stephen D., Committee Chair _________________________________________ John D., Committee Member _________________________________________ Kamala London, Ph., Committee Member _________________________________________ Jason Rose, Ph., Committee Member _________________________________________ John McSweeny, J., Committee Member _________________________________________ Patricia R., Dean College of Graduate Studies The University of Toledo May 2013 Copyright 2013, Aparna A Sahu This document is copyrighted material. Under copyright law, no parts of this document may be reproduced without the expressed permission of the author.
An Abstract of The Roles of Individual Differences and Working Memory in Episodic Memory by Aparna A Sahu Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Experimental Psychology The University of Toledo May 2013 Past studies on strength of handedness, an individual difference variable, and working memory (WM) have shown their independent associations with episodic memory. The current study aimed to check for the associations between these three factors, in addition to assessing the role of strength of handedness in simple and complex WM tasks (measured by digit span and letter number sequencing tasks, respectively) and episodic memory (measured by verbal paired associates). Results revealed robust handedness differences in episodic memory echoing findings from a host of past studies, however, failed to show a significant association with WM. Further, a path model was attempted to check if handedness mediated via WM to influence episodic memory retrieval.
Results revealed that the two were dissociated from one another and yet significantly affected episodic memory. The current findings are explained in the light of past evidence that support the roles of WM and handedness in encoding and retrieving episodic memories, respectively. iii Acknowledgements My sincere gratitude and thanks to my mentor, Dr. Christman, for his constant support and encouragement, and to all committee members for their suggestions, comments and critical questions for this study.
I am also appreciative of Dr. Noela Haughton for offering guidance in applying the statistical model to the current study. I thank the students of UT for participating in this study and being a part of this academic endeavor. Heartfelt thanks to my support system - friends in the department and across the globe, who extended a helping hand and a listening ear when in need; and family members for their continued faith in me.
iv Table of Contents Abstract iii Acknowledgements iv Table of Contents v List of Tables vii List of Figures viii List of Abbreviations ix List of Symbols x I. Individual Differences in Episodic Memory 2 II. Role of Working Memory in Episodic Memory 13 C. Individual Differences in Working Memory 15 III.
Rationale for the Study 18 IV. Statistical Analyses 26 VII. Future Directions 64 References 65 vi List of Tables Table 1 Descriptive statistic data of the measured variables (N = 207) .37 Table 3 Correlation between the episodic memory variables (N = 207) .40 Table 4 Mean and standard deviations and bivariate correlations between variables for the proposed Path analysis model (N = 207) .42 Table 5 Mean (SD) of working memory tasks and strategies factored by handedness groups .48 vii List of Figures Figure 1 Gender differences on mean scores of complex WM as measured by the Letter number sequencing task (LNS) .36 Figure 2 Mean scores across the immediate (T1 to T4) and delayed recalls for the VPA task between handedness groups .38 Figure 3 Gender differences on mean scores on trial one and delayed recall on Verbal paired Associates (VPA).39 Figure 4 Proposed Path model.41 Figure 5 Path model with standardized estimates .43 Figure 6 Re-specified Path model with standardized estimates .45 viii List of Abbreviations AMOS .Analysis of Moment Structures ANOVA .Analysis of Variance CFI .Comparative Fit Index C.Critical Ratio CVLT-II .California Verbal Learning Test – Second Edition DS .Digit Span EHI .Edinburgh Handedness Inventory EEG .Event Related Potential HERA.Hemispheric Encoding Retrieval Asymmetry IBM .International Business Machines Corp.Letter Number Sequencing LTM .Long Term Memory MI.Modification Indices/Index MLE .Maximum Likelihood Estimation PA .Path Analysis PET .Positron Emission Tomography PFC .Prefrontal Cortex RMSEA .Root Mean Square Error of Approximation SAM .Search for Associative Memory SD .Standard Deviation SE .Standard Error SEM .Structural Equation Modeling STM .Short Term Memory TLI .Tucker – Lewis Index VPA.Verbal Paired Associates WAIS-IV .Wechsler Adult Intelligence Scale – Fourth Edition WM .Working Memory WMS .Wechsler Memory Scale WMS-III.Wechsler Memory Scale – Third Edition WMS-IV .Wechsler Memory Scale – Fourth Edition ix List of Symbols β .Statistic for the ANOVA M .Mean score of a sample η2p .Partial Eta square N, n .Squared Multiple Correlation t .T test for two independent samples χ2 .Standard score x Chapter One Episodic Memory A) Introduction Episodic memory refers to a long term memory system that is unique to an individual and is based on past happenings, specific in time and place (Tulving, 1972, 1993). It is a widely studied cognitive process assessed by tests of recall and recognition that makes reference to previously learned material (Friedman & Johnson, 2000).
Behavioral studies have shown a direct relation between greater depth of processing of information at the encoding stage, and greater amounts of retrieval (Craik & Lockhart, 1972) with a greater frequency of “remember” responses than the “familiarity” feeling about responses (Tulving, 1985). Studies have addressed the possible reasons for individual differences in episodic memory performances. In particular, two sets of studies that have provided evidence for these differences and are of interest to the dissertation, are, a) working memory (WM) capacity and, b) the roles of demographic variables such as age, gender and handedness. The following literature review presents findings on the contributions of gender and handedness in both episodic memory and WM, and the role of WM in episodic memory.
This helps further focus on untouched areas that need to be explored such as the role of strength of handedness in simple and complex WM in addition to proposing an extended hypothesis that addresses the combined effects of both strength of handedness (and gender; if gender differences are present in both memory processes) and WM in aiding episodic memory. 1 B) Individual Differences in Episodic Memory Gender/sex: Behavioral studies have most often demonstrated a robust female advantage in verbal episodic memory (Geffen, Moar, O'Hanlon, Clark, & Geffen, 1990; Herlitz, Nilsson, & Backmann, 1997; Herlitz & Rehnman, 2008; Hultsch, Masson, & Small, 1991; Krueger & Salthouse, 2010). Interestingly, other variants of episodic memory, such as visuospatial episodic memory (Lewin, Wolgers, & Herlitz, 2001) and autobiographical memory recall (Rubin, Schulkind, & Rahhal, 1999) have not necessarily reported gender differences. However, Davis (1999) in his series of studies found greater autobiographical memory recall favoring females only when the memory was highly emotional in nature.
Studies that report gender differences suggest that females possess better acquisition abilities, encode information using contextual cues that links separate events to aide recollection (especially autobiographical), make use of more “generation” techniques such as paying attention to more attributes of items to be remembered (e., phonological cues – word rhymes, or associating more meaning to words) that facilitates better recall (Bertsch, Pesta, Wiscott, & McDaniel, 2007; Krueger & Salthouse, 2010). The presence of sex differences in memory processes has been attributed to neurobiological factors. For instance, Mozley, Gur, Mozley, and Gur (2001) in their research showed that dopamine levels in the brain and its uptake in the caudate and putamen found in the subcortical regions was higher in females, which in turn was significantly correlated with performance on a verbal memory task. Some mammalian studies suggest the interplay between sex hormones, particularly estrogen and its production and uptake of certain neurotransmitters in the forebrain areas, and synapse 2 formation in the hippocampal regions, both areas that are strongly implicated in learning and memory (Kimura & Hampson, 1994; McCarthy, Auger, & Perrot-Sinal, 2002; McEwen, 1999).
In terms of neuroimaging evidence, females are reported to have greater gray matter volumes that may be useful in higher order cognitive processes such as memory (Gur, Turetsky, Matsui, Yan, Bilker, Hughett, & Gur, 1999). In another study, although gender differences in episodic retrieval were not present, there were significant differences in the activation levels of certain brain regions during retrieval. Significant differences were noticed in terms of selective increases in the anterior cingulate gyrus in females and in bilateral inferior frontal cortices in males during retrieval (Nyberg, Habib, & Herlitz, 2000). The same authors also found an interaction effect between inferior frontal area activation and memory testing.
Females had a greater activation in this area at retrieval than at baseline however, males showed the opposite effect. This further supports the presence of differential functional neuroanatomical characteristics between the sexes. Handedness: Handedness is considered as an individual difference variable because it represents hemispheric asymmetries which influence cognitive processes (Hellige, 1993). There are two ways of approaching handedness to study cognitive processes: a) Direction of handedness (left versus right handed) and, b) strength of handedness (consistent/strong versus inconsistent/mixed).
Direction of handedness has been used as an indicator of hemispheric asymmetry and its relation to specific cognitive strength of individuals for verbal and 3 visuospatial/nonverbal abilities (e. For instance, right handers are more often left hemisphere dominant for language (e., Knecht, Drager, Deppe, Bobe, Lohmann, Floel, Ringelstein, & Henningsen, 2000). Strength of handedness on the other hand, is in focus because of a strong body of neurological and behavioral evidence that has vouched for its validity. It is considered as a behavioral proxy for interhemispheric communication based on the following set of studies.
Early studies suggested a strong association between increased corpus callosum sizes and inconsistent handedness (Habib, Gayraud, Oliva, Regis, Salamon, & Khalil, 1991; Witelson, 1985; 1989). Around the same time, the Hemispheric Encoding and Retrieval Asymmetry (HERA) model was proposed that showed lateralization differences in verbal episodic memory. Specifically, encoding of verbal episodic memories was associated with the left prefrontal cortex (PFC), and retrieval of the information was associated with the right and/or bilateral prefrontal cortices (Fletcher, Frith, Grasby, Shallice, Frackowiak & Dolan, 1995; Tulving, Kapur, Craik, Moscovitch, & Houle, 1994). The HERA model is additionally confirmed by an event related potential (ERP) study that assessed verbal long term memory (Friedman & Johnson, 2000) and an electroencephalogram (EEG) study that used visuo-spatial contents (Babiloni, Vecchio, Cappa, Pasqualetti, Rossi, Minuissi, & Rossini, 2006).
A recent study showed strong associations between the encoding and retrieval asymmetry in episodic memory and the size of the anterior corpus callosum, further asserting the role of structural connectivity between hemispheres and episodic memory processes with frontal lobe involvement (Kompus, Kalpouzos, & 4 Westerhausen, 2011). Together, these findings provide evidence for the probable role of the corpus callosum in the interhemispheric exchange of information. Given the set of observations between handedness, and the corpus callosum and their roles in episodic memory, behavioral studies were undertaken to explore the association between strength of handedness and episodic memory. These studies have used both non-clinical tests of recall not necessarily normed and are most often an adaptation from past experimental works (e.